1. Field of the Invention
The present invention relates to a driving device that drives a driven member and an optical apparatus including the driving device.
2. Description of the Related Art
A driving device and an optical apparatus have been known which include an actuator (piezoelectric actuator) having a driving shaft attached to a piezoelectric element. For example, JP-A-9-191676, JP-A-11-155292, JP-A-2006-115631, and JP-A-11-318091 disclose driving devices in which a piezoelectric element is expanded and contracted by driving signals and a driving shaft is reciprocated by the expansion and contraction operation of the piezoelectric element to move a driven member that is frictionally engaged with the driving shaft.
The driving device disclosed in JP-A-9-191676 controls the time when a voltage is applied to the piezoelectric element to control the movement speed of the driven member, when driving starts, when driving stops, and when a driving direction is reversed. In the driving device disclosed in JP-A-11-155292, driving waveforms are stored in a memory in advance, one of the stored driving waveforms is selected according to a target driving direction and a target driving speed of the driven member, and a driving speed is controlled by the selected driving waveform. In the driving device disclosed in JP-A-2006-115631, if the movement speed of the driven member is less than a predetermined value, the resonant frequency of the piezoelectric actuator is set to a driving frequency, and the piezoelectric actuator is driven. In the driving device disclosed in JP-A-11-318091, when the driven member is disposed at a predetermined position, a contact pressure reducing leaf spring is used to reduce the contact pressure of the driven member on the driving shaft.
In the driving devices, the driving characteristics of the piezoelectric actuator vary depending on the duration of use and the frequency of use. For example, in some cases, the driven member, which is an object to be moved, is hardly moved at the beginning of moving according to the duration of use and the frequency of use. Therefore, in the driving devices disclosed in JP-A-9-191676 and JP-A-11-155292, it is difficult to perform a desired driving control operation at the beginning of the driven member moving, which may result in an operation error. In the driving device disclosed in JP-A-2006-115631, since the actuator is driven at the resonant frequency, a driving force at the beginning of moving is lowered, which may result in an operation error. In the driving device disclosed in JP-A-11-318091, it is necessary to provide an additional contact pressure reducing unit, which may result in a complicated structure.